As illustrated in prior patents and literature, electric arc welding has heretofore used the average weld voltage and the average weld current for controlling the operation of the power source in the welder. The digital controller includes a digital signal processor (DSP) for controlling a waveform generator or wave shaper that directs the operation of the normal pulse width modulator. This device creates the waveforms successively used by the welder to perform the welding process. Welders regulate the output current or voltage to an average value such as an average weld current by a feedback loop. For a constant voltage process that is welding in the “spray” region, the average current is an accurate gage of the welding process. However, in pulse welding, the average current and average voltage do not accurately reflect the result of the welding process including the deposition rate, heat zone and penetration. This is explained by a example of an ideal pulse welding process, such as one having 500 amperes for 25% of the time and 100 amperes of background current for 75% of the time has an output current of 200 amperes. However, the average current of the welding process merely indicates the deposition rate and does not reflect the true heat input to the welding operation. Consequently, when the welding process is controlled by a series of repetitive waveforms, such as A.C. welding or pulse welding, average current values can not control the heat input. Recently, the welding processes have become quite complex and now often involve a number of successive waveforms, such as A.C. current and pulse current, so the old technology of feedback control for the welding process is not completely accurate and requires a substantial amount of on-site manipulation by a person knowledgeable in welding, especially a person knowledgeable in the new waveform welding procedure using a welder, such as shown in Blankenship U.S. Pat. No. 5,278,390. With the advent of pulse welding using waveform generators and high speed switching power sources, such as inverters, the obtained weld heat has been adjusted by trial and error. Too much heat causes metal to burn through, especially in thin metal welding. Thus, the welding engineer modulates the average current and average voltage to provide the heat input to the welding process to a level so that burn through is theoretically eliminated. This procedure was applicable, however, only for a pure spray type welding process. This procedure of controlling the heat by the average current and average voltage was not applicable to the new generation of electric arc welders where waveforms are changed to control the welding process. This is the new waveform control technology to which the present invention is directed. The old technology used for non-waveform welding is inapplicable to controlling heat in a controlled waveform type welder. The heat is not known by merely reading the voltage and current when the new waveform type arc welders are employed. Consequently, the welding engineer when using waveform control technology changed the base frequency during pulse welding while maintaining a constant or set average voltage. Using this approach of frequency adjustment of a pulse welding procedure while maintaining a constant voltage, the heat could be adjusted by a trial and error technique. When this trial and error procedure was used to modify the waveforms in a new waveform welder, the heat could, indeed, be controlled; however, it was not precise and involves substantial technical knowledge combined with the trial and error procedures.
There is a distinct advantage in pulse welding. This welding process lowers the heat into the joint for the same wire feed speed as a “spray” or “globular” weld process. Thus, a lower heat setting can be set at the factory. The welder had a knob to adjust the nominal frequency, for the purpose indicated above. This change in base frequency did adjust the heat at the welding operation. This resulted in a slight change in the power factor of the welding process through the trial and error method when knowing that the average voltage times average current multiplied by the power factor equals the input heat. Thus, by using a knob to change the base frequency, the power factor was changed to determine heat. However, neither the factory nor the welding engineer at the welding site had the capabilities of directly controlling the power factor. Computation of actual power factor on the fly was not realized in prior control systems and method used for electric arc welders even of the type that used a waveform or wave shape control of the welding process. Consequently, with the introduction of the new waveform welding pioneered by The Lincoln Electric Company, there is a need to control the welding parameters to a value that accurately reflects the heat content. Only in this manner can weld parameters be used in a closed loop feedback system, or otherwise, to control the penetration and heat separately in a weld process using generated waveforms.